The next generation new radio Narrow-Band Internet of Things (NR NB-IoT) is a new radio access technology of the next generation radio access network (RAN) that the 3rd Generation Partnership Project (3GPP) is developing to support a large amount of low-cost device (e.g., 106 devices/Km2) to exchange (e.g., transmit and receive) data in the next generation radio access network (e.g., 5G-RAN). Based on the legacy NB-IoT, which is the NB-IoT specifications designed in 3GPP Release 13 and Release 14 specifications for Internet of Things, the NR NB-IoT is to integrate with the legacy NB-IoT to co-exist with other Radio Access Technologies (RATs) of the next generation RAN, such as the next generation wide band (e.g., 5G-WB) technology. As the next generation wide band (e.g., 5G-WB) RAT uses millimeter wave transmission and reception, which suffer from high path loss, the NR NB-IoT may be used to cover areas within the next generation radio access network (e.g., 5G-RAN) that are not covered by the 5G-WB. That is, the NR NB-IoT may supplement or cover the so-called “wide band holes” within the next generation radio access network (e.g., 5G-RAN). For example, since the next generation wide band (e.g., 5G-WB) cells are relative small (e.g., with a coverage radius of 100 meters), if a user equipment (UE) moves out of the next generation wide band cells and still keeps looking for the wide band cells, the UE may have to frequently conduct cell selection and reselection. The frequent cell selection and reselection are both power inefficient for the UE and a waste of the radio access resources of the wide band cells. Moreover, the NR NB-IoT is to co-exist with legacy Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), and Evolved Universal Terrestrial Radio Access (E-UTRA) networks. Thus, there is a need in the art for methods to handle NR NB-IoT related intra-RAT and inter-RAT procedures. In this disclosure, the intra-RAT and inter-RAT is differentiated based on 5G-RAT, which covers 5G-WB technology and NR NB-IoT technology. A UE switching between 5G-WB cell and NR NB-IoT cell is regarded as an intra-RAT procedure, while switching between a 5G-RAT with other RATs (e.g., E-UTRA) is regarded as an inter-RAT procedure.
In addition, since a NR NB-IoT cell may cover a relatively large area (e.g., with a coverage radius of several kilometers) as compared to a next generation wide band cell (e.g., a 5G-WB cell), the NR NB-IoT needs to provide different coverage enhancement (CE) levels/labels based on the signal strength seen by the UEs in the NR NB-IoT cell. For example, the CE levels/labels may indicate how many times the UE or its serving base station needs to repeat the transmission to mitigate the inefficiency of the control and/or data channel. For example, according to the 3GPP Release 13, in legacy NB-IoT, a UE needs to conduct a signal strength measurement by itself to estimate an appropriate CE level/label to decide on, among other things, the CE label's range, the associated UE resource for transmission, and how many times the UE needs to repeat the control and/or data signal. However, the CE level/label estimated by the UE may not be sufficiently accurate to ensure a successful transmission from the UE to the legacy NB-IoT. This is because the uplink channel condition as seen by the legacy NB-IoT base station may be worse than the downlink channel condition as seen by the UE, which is reflected in the CE level/label based on the UE's measurement. Thus, in light of introduction of the NR NB-IoT in the next generation radio access network (RAN), there is a need in the art for methods to provide accurate coverage enhancement levels/labels to handle NR NB-IoT related intra-RAT and inter-RAT procedures.
Furthermore, in a next generation radio access network (e.g., 5G-RAN), a UE may transition from an RRC connected state to an RRC inactive state or an RRC idle state, where the UE may take measurements to perform cell selection and cell reselection, even when the UE is in the RRC idle or RRC inactive state. For the RRC state transitions, an RRC suspend message and an RRC Resume message may be used. For example, in a next generation radio access network (e.g., 5G-RAN), the RRC Suspend message may inform a UE that the serving base station (e.g., a next generation node B (gNB)) will release the RRC connection, but will retain the UE context. When there is a need for packet exchange, the UE can quickly send a RRC Resume message, so that the UE and serving base station can resume an RRC connection for data/control signal transmission to reduce latency and radio access overhead.
Thus, in light of introduction of the NR NB-IoT in the next generation radio access network (RAN), there is a need in the art for methods to handle NR NB-IoT related intra-RAT and inter-RAT RRC resume procedures for mobility enhancement.